1. Field of the Invention
The present invention relates to a device for rotating spindles for use in a wood working machine and more particularly, to a means for rotating tools for use in a NC (Numerical Control) router which works on woods, plastic, stones and the like.
2. Description of the Prior Art
A cutting tool for use in a working machine of this kind needs to be rotated up to about 30,000 revolutions per minute and also, a wide range of rotational speed, i.e., 2,000 to 25,000 rpm, is practically necessary. For this purpose, a high-frequency motor or the like is exclusively employed as a means for rotating the cutting tool, which controls the rotational speed by changing the frequency. However, such high-frequency motor requires ancillary devices such as a frequency changer, a field control transformer and the like, thereby increasing the cost thereof.
Multi-shaft heads (turret heads and parallel heads) have recently been developed for the NC router as disclosed in U.S. Pat. No. 4,313,478 to Y. Suzuki from the standpoint of productivity and operating efficiency. In this case, however, a corresponding number of high-frequency motors is required in association with each tool. Thus, a high-grade router may not be provided at low cost.